Embodiments of the present invention relate to acidic milk products having improved stability. In particular, embodiments of the present invention relate to acidified milk products comprising a pectin stabilizer system.
Fermented milk products are among the most widely consumed foods in the world today, enjoyed by peoples of nearly all cultures and backgrounds. Yogurt (a milk product fermented with L. bulgaricus and S. thermophilus that typically has a pH of less than 5.0) is one of the most well-known fermented milk products.
Although yogurt remains a very popular comestible item, there also is a growing demand for liquid yogurt drinks. These yogurt drinks have the advantage of being more portable, convenient, and easier to consume than yogurt. In addition to yogurt drinks, other drinkable products containing milk as an ingredient, but with lower pH than fresh milk, also are popular. The low pH may, for example, result from blending milk with fruit products like orange or strawberry juice. The commercial versions of such drinks are typically heat-treated for obtaining a long shelf life.
Yogurt drinks often make use of stabilizers, such as pectin, against sedimentation of the milk solids that are found in the yogurt. Although pectin is a particularly good stabilizer at pH's of between 3.7 to 4.3, which are typical for commercial yogurt drinks providing excellent stabilization of milk solids, pectin may lose its efficacy for pH's between 4.3 to 5.4. Thus, as the pH of the acidified milk drink increases, the pectin becomes less effective as a stabilizer. In particular, pectins that are effective at stabilizing against sedimentation of milk solids at pH's between 3.7 to 4.3 may be required in significantly greater dosages to stabilize the milk solids with increasing pH, and may cause the acidified milk drink to become unacceptably thick. The increased thickness may occur at least in part due to the neutralization of the carboxylic acid groups on the pectin, as well as on the protein particles, by the protons, decreasing the surplus positive charge of the protein particles and increasing the tendency for the pectin to self-associate with Ca2+ ions.
Not wishing to be bound by any theory, it is believed that protein protection may prevent aggregation of the milk proteins during acidification and thermal processing of the beverage. The proteins found in neutral pH milk are relatively small in micellular size and possess a net negative charge that allows the particles to repel one another and remain in solution. For example, caseins are protein micelles having spherical diameters of about 20 to 400 nm. As micelles, the caseins remain in colloidal form, suspended in the milk. However, maintaining the colloid state is dependent on the pH of the suspension. At a pH of about 5.0 (or even as high as 6.5 for a milk drink subjected to heat treatment), the casein starts to lose coherence and begins to precipitate out of the suspension. At a pH of about 4.5, precipitation of the casein is complete. Thus, for milk products formulated to a pH below 5.0 (such as yogurt and yogurt drinks) the casein particles are present in their precipitated phase rather than as colloidal micelles. Accordingly, pectin or other stabilizers may be required in milk drinks having an acidic or mildly acidic pH in order to prevent the casein particles from precipitating out of the milk and forming sediment.
Although beverages produced at the foregoing pH may be acceptable to some consumers, many consumers desire a more mildly acidic beverage having a less-tart taste. Accordingly, there is a need in the art for an acidified milk drink that is stable under mildly acidic conditions while still retaining a suitable consistency for consumers to drink.